The present invention relates to a washing machine or an apparatus having a rotatable container.
Washing machines are provided with various kinds of sensors and detectors such as: a load detector for detecting the weight of the laundry contained in a wash-and-extraction tub (which is referred to as xe2x80x9claundry tubxe2x80x9d); a level sensor for measuring the water level in the laundry tub; and a vibration sensor for detecting an abnormal vibration which occurs in the course of an extracting process if the laundry tub is rotated with the laundry being distributed unevenly.
Japanese Unexamined Patent Publication No. S63-206283 discloses one of conventional methods of detecting the weight of the laundry. The method includes steps of:
turning on a motor for rotating a pulsator provided at the bottom of the laundry tub with no water held in the tub and then turning off the motor after a preset time period; counting pulse signals produced synchronously with the rotation of the motor after the motor is turned off;
and calculating the weight of the laundry based on the number of pulses produced until the motor stops the inertial rotation. In this process, the pulsator stops sooner as the weight of the laundry is larger. Accordingly, the weight of the laundry is determined larger as the number of pulses is smaller. By such a method of detecting the weight of the laundry utilizing the inertial rotation of the pulsator, however, it is difficult to improve the accuracy of detection because the detected value varies depending on the quality or condition of the fabric of the laundry. Another problem is that the laundry is often damaged due to the friction between the pulsator and the laundry.
In some of the conventionally proposed methods, a weight sensor is used for directly measuring the weight of the laundry contained in the washing tub, instead of detecting the weight indirectly. For example, Japanese Unexamined Patent Publication No. H5-84382 discloses a washing machine, where a weight sensor composed of a spring, coil, core and other elements is provided on suspension rods with which the washing tub is suspended. According to this construction, when the load on the suspension rods change and the suspension rods move up or down, the length of the part of the core in the coil held at a fixed position changes, and the inductance of the coil changes accordingly.
When the above-described weight sensor is used, however, the damping design becomes complicated because two types of spring (one for damping and the other for detecting weight) are provided at one or some of the suspension rods while a single spring is provided at other rods. Also, the weight sensor itself may increase the vibration, because the spring used in the weight sensor has its own natural frequency. Also, the use of the above described weight sensor is not preferable in respect of designing the washing machine with smaller size and greater capacity, because the weight sensor is normally large in size so that it occupies a substantial space in a body housing of the washing machine. Also, the characteristics of the spring of the weight sensor changes or deteriorates as the spring ages, which deteriorates the detection accuracy.
Another problem concerning the weight sensor is as follows. In the above-described washing machine, the weight sensor is used for detecting not only the weight of the laundry contained in the laundry tub but also the weight of water supplied and held in the outer tub. The weight of the laundry is several kilograms at most, while that of water held in the outer tub is almost ten or more times as great as that of the laundry. When the weight sensor is designed to detect a weight as great as several tens of kilograms, the detection accuracy of a weight as small as the weight of the laundry becomes inevitably low. When, on the other hand, the weight sensor is designed to detect a weight as small as the weight of the laundry with adequately high accuracy, the maximum weight that the weight sensor can detect cannot be as great as that of the water held in the outer tub. Thus, it is difficult to detect both the weight of the laundry and that of water held in the outer tub with the above-described weight sensor.
Taking account of the above-described problems, one object of the present invention is to provide a washing machine with a small-sized load sensor having high detection accuracy without introducing difficulties in the damping design and without causing unfavorable effect on the rotation of the laundry tub. Another object of the present invention is to utilize the load sensor not only for detecting the weight of the laundry but also for detecting the weight of water and further for detecting water level in the outer tub. Still another object is to provide a washing machine having a sensor whereby the vibration of the laundry tub and/or the outer tub is detected with high accuracy during the extracting process where the laundry tub spins at high speed.
For solving the above-described problems, a washing machine according to the present invention utilizes a pressure sensor constructed with a magnetostrictive element whose magnetic characteristic changes depending on the changing rate or magnitude of an external force exerted on it. A pressure sensor of this type is disclosed, for example, in the full text of Japanese Unexamined Utility Model Publication No. H1-105834.
Thus, in a washing machine including a body housing, an outer tub suspended in the body housing and a wash-and-extraction tub rotatably provided in the outer tub, the washing machine according to a first aspect of the present invention (which is referred to as xe2x80x9cfirst washing machinexe2x80x9d in this specification) includes a pressure sensor placed at a position where it experiences an external force due to the weight of the laundry contained in the wash-and-extraction tub and the weight of water held in the outer tub. The pressure sensor is constructed with a magnetostrictive element on which the external force is exerted and a coil placed close to the magnetostrictive element. The coil is used for detecting a change in the magnetic characteristic of the magnetostrictive element due to the external force. A measuring part receives an output of the coil of the pressure sensor and measures the weight of the laundry and the weight of the water based on the output. An operation controller controls the water supply into the outer tub based on the weight measured by the measuring part. First, before the start of the water supply, the operation controller determines an object amount of water to be supplied into the outer tub according to the weight of the laundry. Next, while the water is being supplied, the operation controller monitors the weight of water with the measuring part and controls the water supply with respect to the object amount of water.
The above-described pressure sensor is advantageous in that it is small and lightweight, and that it has a broad detection range. Since it occupies a very small space, the pressure sensor can be placed anywhere in the washing machine and allows designing washing machines of smaller in size and greater in capacity. Also, the pressure sensor never functions as a source of vibration because it includes no moving element such as a spring. Since no moving element is used, further, detection accuracy never deteriorates due to degeneration of the moving element.
The above-described pressure sensor has such an advantage that it can detect a broad range of external force and that its sensitivity is higher as the external force is smaller. Therefore, when it is desired to measure both the weight of the laundry and the weight of water with a single pressure sensor, the above-described sensor may be preferably used. For example, based on the output of the above-described pressure sensor, the measuring part not only measures the weight of the laundry with high sensitivity before water is supplied, but also measures the weight of water, which increases beyond the weight of the laundry after the water is supplied. The weight of water can be translated into water level held in the outer tub. Thus, the measuring part with the pressure sensor not only functions as a load detector but also as a level sensor, so that there is no need to provide a conventional level sensor using a pressure hose or other devices.
The above-described pressure sensor may be placed at such a position where it experiences not only an external force due to the weight of the laundry and the water, but also another external force resulting from an eccentric load due to an uneven distribution of the laundry contained in the laundry tub and a vibration of the laundry tub due to the eccentric load. According to such a construction, the measuring part can measure not only the weight of the laundry and the water, but also the eccentric load and the vibration due to the eccentric load, based on the output of the pressure sensor.
The measuring part may be constructed so that it measures only the eccentric load and/or the vibration based on the output of the coil of the pressure sensor.
In a mode of the first washing machine, the measuring part is constructed so that the change in the magnetic characteristic of the magnetostrictive element is detected by a change in the inductance of the coil. For example, it is detected by a change in the oscillation frequency of an LC oscillator including the coil. In general, the inductance of a coil changes depending on the number of turns of the coil. When the change in the inductance of the coil is detected as described above, the amount of change in the inductance varies according to the number of turns. Thus, as for the present case, it is preferable to provide a plurality of coils constructing a coil assembly whose inductance is variable by selecting one, some or all of the coils. According to this construction, the sensitivity of the pressure sensor can be arbitrarily determined according to an object to be detected by selecting one, some or all of the coils.
For example, when the weight of the laundry and the weight of water are detected using the same pressure sensor as described above, the weight of the laundry is detected with higher sensitivity, and the weight of water is detected with lower sensitivity.
In the first washing machine, the pressure sensor may be located at various places in the washing machine, as explained above. For example, the pressure sensor may be provided in at least one of the rod holders which hold the suspension rods, or in at least one of the feet supporting the washing machine on the floor. For detecting the weight of the laundry and the weight of water, it is preferable to provide the pressure sensor in the rod holder or in the foot because these parts are directly affected by the external force due to the weight of the laundry and the weight of water.
It is preferable to provide the pressure sensor in every rod holder or in every foot of a washing machine and measure the whole weight based on the outputs of all the pressure sensors. By this construction, the detection accuracy is improved.
It is not essential for the present invention to provide the pressure sensors in all of the plural rod holders or feet. For example, the weight of the laundry, the weight of water, the eccentric load or the vibration may be inferred based on the output of a single pressure sensor provided in one of the plural rod holders or feet. According to such a construction, the production cost is reduced. Under such a construction, it is further preferable to detect the weight a plurality of times while rotating the laundry tub at low speed and infer the weight of the laundry, the weight of water, the eccentric load or the vibration based on the plurality of detected values. According to such a construction, even though all the suspension rods or feet are not provided with the pressure sensor, the undesirable effect of the unbalance in the distribution of the weight of the laundry is cancelled, so that a high detection accuracy is obtained.
In the first washing machine, when only the eccentric load and/or the vibration is detected, the pressure sensor is preferably placed at such a position where the vibration appears with a large magnitude in the course of the washing, rinsing or extracting process. For example, the pressure sensor may be attached to the body housing. In this case, the vibration of the body housing is converted into an external force, which exerts on the pressure sensor and is detected by the pressure sensor.
In a washing machine including a body housing, an outer tub suspended in the body housing and a wash-and-extraction tub rotatably provided in the outer tub, the washing machine according to a second aspect of the present invention (which is referred to as xe2x80x9csecond washing machinexe2x80x9d in this specification) includes a pressure sensor placed at a position where it experiences an external force due to the load on the outer tub and the vibration of the outer tub. The pressure sensor is constructed with a magnetostrictive element on which the external force is exerted and a coil placed close to the magnetostrictive element. The coil is used for detecting a change in the magnetic characteristic of the magnetostrictive element due to the external force. A measuring part receives output of the coil of the pressure sensor and measures the load on and vibration of the outer tub.
The measuring part of the second washing machine may be constructed so that its measuring mode is selectable between a weight-measuring mode for measuring the load on the outer tub and a vibration-measuring mode for measuring the vibration. For example, the measuring part is constructed to run in the vibration-measuring mode while the laundry tub is rotating and to run in the weight-measuring mode when the laundry tub is halted. According to such a construction, abnormal rotation is detected with the measuring part in the vibration measuring mode during the rotation of the laundry tub, while the weight of the laundry is measured by the measuring part in the weight-measuring mode when the laundry tub is halted, particularly at the beginning of the operation.
The washing machine may be constructed so that the rotation is determined as abnormal when the magnitude of the vibration measured by the measuring part is greater than a preset threshold value. When the laundry tub rotates with an eccentric load due to uneven distribution of the laundry or other factors, the magnitude of vibration measured by the measuring part is greater as the amount of eccentricity is greater. So, the abnormal rotation can be detected based on the magnitude of vibration.
The above-described washing machine may be preferably constructed to determine the threshold value based on the load on the outer tub measured by the measuring part in the weight-measuring mode. Even when the amount of eccentricity is equal, the magnitude of vibration measured by the measuring part varies depending on the weight of the laundry. Taking this into account, the threshold value is determined based on the load on the laundry tub, whereby the instability in the threshold value of the eccentricity is reduced and the determination of abnormal rotation becomes more reliable.
The measuring part of the second washing machine may be constructed to have a weight-and-vibration-measuring mode for measuring the load on the outer tub and the vibration of the outer tub at the same time. With such a construction, the washing machine may be provided by a controller that determines a threshold value based on the load measured by the measuring part and determines the rotation as abnormal when the magnitude of vibration is greater than the threshold value. According to such a construction, the magnitude of the load for determining the threshold value is obtained simultaneously with the magnitude of vibration which is the object of the abnormal rotation detecting process. Thus, the threshold value is determined without being influenced by a time variability of the load.
When the outer tub is suspended by plural suspension rods, the pressure sensor may be provided in at least one of the suspension rods in such a manner that an end of the pressure sensor is received by an end of the suspension rod and the other end of the pressure sensor is received by the body housing. Any suspension rod equipped with the pressure sensor may further comprise a projection extending from the suspension rod toward the outer tub. According to such a construction, when the laundry tub rotates abnormally or eccentrically due to uneven distribution of the laundry, the outer tub tilts and collides with the projection.
The shock of the collision is transmitted to the pressure sensor via the suspension rod, so that the abnormal rotation is detected from the output of the pressure sensor. It is preferable to form the side wall of the outer tub thicker at the part where the side wall collides with the projection than elsewhere, so that the dent or wear of the outer tub is alleviated.
When the present invention is applied to a washing machine having a pulsator for producing water current in the outer tub, the washing machine may be constructed so that the speed of the pulsator is decreased to weaken the water current when a vibration of magnitude greater than a preset level is detected in the course of the washing or rinsing process. Such a construction is preferable in that not only the vibration is reduced but also the water is prevented from being scattered around the washing machine. Also, the washing machine may be constructed so that an unbalance-correcting operation is carried out for redistributing the laundry in the laundry tub when a vibration of magnitude greater than a preset level is detected with the pressure sensor during the extracting process.
It should be noted that the present invention is applicable not only to the washing machine as described above but also to other types of apparatuses having a container which is rotatable about a horizontal or vertical axis, similar to the washing machine. Thus, an apparatus according to the present invention is constructed so that a pressure sensor constructed with a magnetostrictive element is provided at a position where the pressure sensor experiences an external force due to a load on the container or a vibration resulting from the rotation of the container. When the present invention is applied to a drying machine having a rotatable drum, the weight of the laundry in the drum is detected, and the vibration is detected during the operation.